With respect to radiation measurement devices that are placed in nuclear power plants, nuclear fuel reprocessing plants, plants utilizing radiation and the like, and at around these plants, in order to cover at the time of measuring a dose rate, etc., a wide measuring range from a usual radiation level up to a radiation level based on the accident scenario, these devices are each required to use, for example, an ionization chamber as a radiation detector, and to accurately measure a detection current signal which is generated by the action of radiation in the ionization chamber and is extremely small, widely ranging from an order of 10−13 A (ampere) to an order of 10−7 A. In order to measure such an extremely small current, the detection current signal is converted, in a state where insulation is highly maintained, into an output signal resistant to noise, which is then measured, and the measured value is outputted after converted into an engineering value such as a dose rate, etc. (see, for example, Patent Documents 1, 2)
Further, the radiation measurement devices are required to fulfill the requirement of “when there is no radiation source capable of checking the detector, integrity of the measuring system shall be confirmed in such a manner that a simulation signal is inputted as an input to the electronic circuit in the test mode” described in Guideline for Radiation Monitoring of Nuclear Power Plants, JEAG4606-2003 (see, for example, Non-Patent Document 1).